CVE-2026-23890: pnpm scoped bin name Path Traversal allows arbitrary file creation outside node_modules/.bin

Summary A path traversal vulnerability in pnpm's bin linking allows malicious npm packages to create executable shims or symlinks outside of nodemodules/.bin. Bin names starting with @ bypass validation, and after scope normalization, path traversal sequences like ../../ remain intact.

Details The vulnerability exists in the bin name validation and normalization logic:

1. Validation Bypass (pkg-manager/package-bins/src/index.ts)

The filter allows any bin name starting with @ to pass through without validation:

typescript .filter((commandName) => encodeURIComponent(commandName) === commandName || commandName === '' || commandName[0] === '@' // <-- Bypasses validation )

2. Incomplete Normalization (pkg-manager/package-bins/src/index.ts)

typescript function normalizeBinName (name: string): string { return name[0] === '@' ? name.slice(name.indexOf('/') + 1) : name } // Input: @scope/../../evil // Output: ../../evil <-- Path traversal preserved!

3. Exploitation (pkg-manager/link-bins/src/index.ts:288)

The normalized name is used directly in path.join() without validation.

PoC 1. Create a malicious package: json { "name": "malicious-pkg", "version": "1.0.0", "bin": { "@scope/../../.npmrc": "./malicious.js" } }

2. Install the package: bash pnpm add /path/to/malicious-pkg

3. Observe .npmrc created in project root (outside nodemodules/.bin).

Impact - All pnpm users who install npm packages - CI/CD pipelines using pnpm - Can overwrite config files, scripts, or other sensitive files

Verified on pnpm main @ commit 5a0ed1d45.